Generally, the operation of a sample introducing device of a trace detecting instrument in the prior art includes inserting an exterior test paper into a sample introducing device after being wiped. Sampling and introducing are separated during the whole processes, which requires a high demand on the thickness and width of the test paper adapted to the sample introducing device and the operation of inserting paper. If a design deviation exists at a paper inserting opening of the sample introducing device or an angle deviation exists during assembly, it will easily cause paper jams or difficulties in paper inserting. Moreover, it is difficult to remove a test paper that is damaged and remains in the sample introducing device, such that a sample detecting effect is influenced and the difficulty of later maintenance is increased. In addition, due to a high accuracy requirement of machine process for the sample introducing device in the prior art, it is hard to process and a high cost is also a problem.